Silicon mechanical polishing

Li, S. H. and Miller, R., Chemical Mechanical Polishing in Silicon Processing, Semiconductor Semimet., Vol. 63, New York Academic Press, 2000. 

Zhao, Y. W. and Chang, L., AMicro-Contact, and Wear Model for Chemical-Mechanical Polishing of Silicon Wafers, Wear, Vol. 252,2002, pp. 220-226. 

In the early days of silicon device manufacturing the need for surfaces with a low defect density led to the development of CP solutions. Defect etchants were developed at the same time in order to study the crystal quality for different crystal growth processes. The improvement of the growth methods and the introduction of chemo-mechanical polishing methods led to defect-free single crystals with optically flat surfaces of superior electronic properties. This reduced the interest in CP and defect delineation. 

The crosslinked ViSi (OCH,), silicone type substrates were spread with a microslide on a mechanically polished copper sample to form several tens of pm thick films. Then, they are transferred into the spectrometer chamber without passing through the atmosphere. 

Hu YZ, Yang G-R, Chow TP, Gutmann RJ. Chemical-mechanical polishing of PECVD silicon nitride. Thin Solid Films 1996 290-291 453-455. 

Mullany B, Byrne G. The effect of slurry viscosity on chemical-mechanical polishing of silicon wafers. J Mater Process Technol 2003 132 28-34. 

Zhao Y, Chang L. A micro-contact and wear model for chemical-mechanical polishing of silicon wafers. Wear 2002 252 220-226. 

Choi W, Lee S-M, Singh R. Further investigation of effects of ph on silicon dioxide chemical mechanical polishing (CMP). The Electrochemical Society 204th Meeting 2003. 

Nanoindentation techniques were used to determine the hardness of Cu, Ta W metal discs and thin films on silicon substrates as a function of load or indentation depth. Cu films exposed to oxidizing solutions containing H2O2 exhibited a higher hardness at the surface while no such change was observed for W exposed to ferric nitrate. The implication of these measurements and their relationship to chemical-mechanical polishing rates are discussed. 

This paper has summarized some of the results related to the fluid pressure distribution between a hard (steel) surface and a soft compliant (polyurethane) surface. The results are pertinent to the mechanical aspects of chemical mechanical polishing of silicon. The results show that the model can predict a subambient pressure. This is due to the fact that the leading edge of the wafer squeegees the slurry, and the stress distribution beneath the wafer is non-uniform. 

FIGURE 2.30. Mott-Schottky plots in 5% HF for mechanically polished n-type silicon and chemically etched sample. After De Mierry et a/. "... 

Metal-RIE process was/is used in the fabrication of Al inter-coimects on chips." This process is depicted in four steps in Fig. 2. The first step in the metal-RIE process is sputter deposition of a blanket thin film of Al (or Al alloys, such as Al-Cu, Al-Si) over a planerized dielectric (e.g., silicon dioxide). In the next step, the unwanted metal is etched away by reactive ion etching (RIE) through a photoresist mask. The features produced this way are separated, electrically isolated, metal Al conductor lines. In the RIE process chemicaly active ions such as F or Cl bombard the Al surface and form volatile aluminum fluorides or chlorides, which are then pumped away in the vacuum system. After etcliing, a dielectric is deposited in such a fashion that it fills the gaps between the lines as well as above them. In the last step, the dielectric is planarized using the chemical mechanical polishing (CMP) technique. ... 

Contamination Studies. Schmidt and Pearce (22,). in a classic study, using NAA evaluated sources of contamination of silicon during device processing. Their work demonstrated clearly that high-temperature oxidation steps are particularly likely to add transition-metal contaminants. Mechanical polishing compounds, boats and handling tools, and components of ion-beam equipment were also identified as being potentially troublesome. 

---